Medical electrodes provide an electrical interface between a patient and monitoring equipment (e.g., an electrocardiograph device) or between a patient and stimulating equipment (e.g., interferential and iontophoresis devices). A specific type of stimulating electrode, used to provide an electrical interface between a patient and defibrillation equipment, must be capable of conducting the high-energy level required for transcutaneous defibrillation.
In a malady called “fibrillation,” the normal contractions of a muscle are replaced by rapid, irregular twitchings of muscular fibers (or fibrils). Fibrillation commonly occurs in the atria or ventricles of the heart muscle; the normal, rhythmical contractions of the heart are replaced by rapid, irregular twitchings of the muscular heart wall. A remedy for fibrillation is called “defibrillation,” a procedure which applies an electric shock to arrest the fibrillation of the cardiac muscle (atrial or ventricular) and restore the normal heart rhythm.
Defibrillation electrodes deliver high-energy levels required for defibrillation, up to 360 Joules or more. Defibrillation electrodes also distribute the energy over a relatively large area of the epidermis of the patient to achieve adequate current density distribution within the atria or ventricles. Well-defined industry standards exist for defibrillation electrodes. In particular, the American National Standards Institute (ANSI) standards for defibrillation electrodes have been published by the Association for the Advancement of Medical Instrumentation (AAMI). The ANSI standards for the size of defibrillation electrodes recommend, for example, that the minimum active area of individual, self-adhesive electrodes used for adult defibrillation and pacing shall be at least 50 cm2 and that the total area of the two electrodes shall be at least 150 cm2.
The specification for defibrillation recovery characteristics, which describes certain time-related, electrical dissipation properties of the electrode following repeated electrical shocks of defibrillation currents, is difficult for many electrodes to meet. The use of non-compliant electrode may result in life-threatening delays following defibrillation. This restriction limits the usefulness of such electrodes in a critical care environment. Accordingly, many of these products bear a caution label that they are not to be used where defibrillation is a possibility.
Irritation and burning of the patient's skin due to high current density around the perimeter of the electrodes and uneven current distribution is a common problem with defibrillation electrodes, particularly after application of repeated high-level defibrillation or cardiac pacing pulses. A new disposable medical electrode, particularly useful for high-energy applications, is disclosed here. The invention provides an electrode that features control of current distribution. In addition, the electrode provides energy sufficient for defibrillation, and which has improved current distribution between the electrode and the skin surface of the patient to efficiently deliver the energy without burning the patient's skin.